[XrdEC] Add README file.

src/XrdEc/README

@@ -0,0 +1,30 @@
+To build XRootD with with XrdEc:
+
+    following build dependencies are required: autoconf, automake, libtool, yasm
+    following flag needs to be passed to cmake: -DENABLE_XRDEC=TRUE
+
+The OFS plug-in needs to send following redirect response in order to activate the default EC plug-in in the xrootd client:
+
+   if( error.getUCap() & XrdOucEI::uEcRedir )
+   {
+     const char *redirec = "root://ec-gateway.cern.ch//tmp/file.out?"
+                           "xrdec.nbdta=4&"
+                           "xrdec.nbprt=2&"
+                           "xrdec.blksz=1024&"
+                           "xrdec.plgr=file:///data/dir00/,file:///data/dir01/,file:///data/dir02/,file:///data/dir03/,file:///data/dir04/,file:///data/dir05/,file:///data/dir06/,file:///data/dir07/&"
+                           "xrdec.objid=00000001&"
+                           "xrdec.format=1&"
+                           "xrdec.dtacgi=sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC&"
+                           "xrdec.mdtacgi=sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC,sign=123ABC&"
+                           "xrdec.cosc=true&"
+                           "xrdec.cksum=crc32c&""
+                           "xrdec.chdigest=crc32c"& // optional
+                           "xrdec.nomtfile=false";  // optional
+     error.setErrInfo(~( kXR_ecRedir ), redirec);
+     return SFS_REDIRECT;
+   }
+
+If xrdec.cosc=true, the client will send an opaque query to commit the file on successful close:
+
+   ?xrdec.objid=00000001&xrdec.close=true&xrdec.size=4096&xrdec.cksum=adler32:cbec9df1
+